Balloons are widely used on medical devices, such as catheters, employed in various medical treatments. Examples of such treatments include repair of the vascular system, e.g. angioplasty, stent placement, and the like and in treatment and repair of disorders of the gastrointestinal, bronchial or esophageal tracts. Such balloons may be made of a wide variety of materials. With some of these materials, namely polyamides (xe2x80x9cnylonsxe2x80x9d), polyurethanes and block copolymers comprising polyamide or polyurethane segments, hydrogen bonding between chains of the molecule plays a significant role in the strength profile of the formed balloon.
U.S. Pat. No. 4,906,244 issued in March 1990 to Pinchuk et al describes balloons of certain aliphatic polyamides and states that xe2x80x9cnylon materials have been observed to exhibit desirable stability during processing to the extent that they do not absorb excessive moisture from the environment if the parison is allowed to stand uncovered for reasonable time periods.xe2x80x9d
U.S. Pat. No. 5,328,468 describes medical device balloons made of an aromatic polyamide.
U.S. Pat. No. 5,556,383 describes medical device balloons made of a block copolymer comprising polyamide segments.
EP 0592885 describes medical device balloons made of a thermoplastic polyurethane.
U.S. Pat. No. 5,714,110 describes an improved method of preparing an oriented balloon of thermoplastic material comprising extruding a hollow tube of the thermoplastic material and subsequently expanding the tube by subjecting the tubing, while in a mold, to an elevated temperature and an increased interior pressure to produce an oriented balloon, the invention being characterized in that the tube is subjected to a drying step, prior to the expanding step, thereby increasing the strength of the balloon relative to a reference balloon prepared in the same manner, except for said drying step.
Hence until now it has been considered that the moisture content of a parison of thermoplastic polymer material used to form a medical balloon was not a particular concern, or that if it was a concern, the parison should be dried before blowing the parison into a balloon.
In forming balloons by radial expansion of a tubular parison it is often necessary to use a very high blowing pressure to initiate radial expansion at conventional blowing temperatures of about 90xc2x0 C. to about 110xc2x0 C. Once initiated, however, the high pressure causes very rapid growth as the polymer material gets increasingly thinner, until the expanding polymer material reaches the mold wall. This rapid growth has been associated with a number of common defect problems, such as balloons displaying xe2x80x9cfish eyexe2x80x9d defects.
In copending U.S. application Ser. No. 09/672,330, filed Sep. 28, 2000, it is taught that a slower balloon growth rate can reduce fish eye defects, but the technique of obtaining a lowered growth rate in that application requires modification of parison configurations.
It has now surprisingly been discovered that significant benefits can be obtained in forming a balloon from a parison of a thermoplastic polymer which undergoes substantial intermolecular hydrogen bonding, when the parison is conditioned in a high humidity environment prior to blowing the balloon. Accordingly the invention in one aspect is a process for blowing a balloon from a tubular parison of a thermoplastic polymer by radially expanding the parison at an elevated temperature and pressure, the process characterized in that:
a) the polymer is one which undergoes hydrogen bonding between at least some segments thereof (xe2x80x9ca H-bonding polymerxe2x80x9d);
b) the parison is conditioned in a high moisture environment prior to blowing, and
c) the balloon is blown after moisture conditioning of the parison and without an intervening drying thereof.
Moisture conditioning is continued for a time sufficient to obtain a stable reproducible high moisture content, suitably about 8 hrs or more in an environment of at least 80% RH.
Further aspects of the invention will become apparent from the detailed description which follows.